There exists a variety of low-temperature storages for storing fresh foods such as vegetables, fish, and other kinds of foods. Such storages include freezers, refrigerators, and other types of low-temperature cases. Due to recent needs for commercial refrigeration devices for storing a large quantity of varied foods, there are many types of refrigerators.
They are commonly known as freezers, refrigerators, and so-called combination refrigerators which comprise a combination of freezers and refrigerators operable at different temperatures appropriate for the goods stored therein. Therefore, such combination refrigerators conventionally required specially designed controllers suitable for their particular uses.
However, in actuality, such a conventional controller is designed on a compromise to operate at an average operating condition, based on such parameters as defrosting time (including starting time and period of defrosting), alarm conditions (such as critical abnormal temperature and permissible duration of abnormality), defrosting method (including types of defrosting heaters and period of off thermo-cycle defrosting), and chamber temperatures, so that it may be roughly applicable for all types of combination refrigerators, since designing and manufacturing varied types of controllers is inefficient and costly. Furthermore, if varied types of controllers are manufactured, their maintenance involving various repair components is cumbersome.
Since such refrigerators are not designed for optimum conditions, their operation often suffers inefficiency.
The controllers used with these conventional refrigerators are designed basically for use with one chamber, so that they cannot be used for a combination refrigerator having more than two chambers. Use of more than two controllers in a combination refrigerator is not only disadvantageous but also inadequate when more than two chambers are required to operate at different refrigeration temperatures, since no convenient means has been available for maintaining each of the chambers at a temperature specified. Therefore, a conventional combination refrigerator requires as many control systems as the combination of the temperatures used.
These professional freezers, refrigerators, and combination refrigerators having a plurality of refrigerating chambers are used in certain particular temperature ranges for specific purposes.
In these cases temperature indicators are used for indicating the preset temperature as well as the current temperature of a chamber by selecting one of possible indication modes. Such a double purpose indicator may indicate the preset temperature by, for example, a first push of a push button switch, and the current chamber temperature by a second push. However, after a number successive switchings, one may often lose keeping track of the current status of the switch. In order to avoid such inconvenience an indicator or a lamp is normally provided to notify the operator the status of the switch.
However, this type of temperature indication has disadvantages that, for example, the provision of the indicator lamp adds some limitation to the design of the controller and an extra indication circuitry is need for the indicator.
It is often the case that abnormal thermal conditions take place in the refrigeration chambers during refrigerating operation. Conventionally, such abnormality is indicated by a common alarm indicator or a set of alarm indicators provided one for each chamber.
Although such a conventional alarm system may indicate the abnormality, it cannot, in the case of common indicator, point out the specific chamber suffering from the abnormality until each chamber temperature is compared with its preset preset temperature, requiring cumbersome procedures. On the other hand, the use of alarm indicators provided for individual refrigeration chambers requires the same number of indicators as the number of the chambers. This in turn requires many circuits and components, and might fail to attract operator's due attention.